Throughout the 1970s, the Trans Am continued as the top of the Firebird line. As other manufacturers killed off their performance cars in the name of increased economy, Pontiac added the 455 Super Duty in 1973-1974—widely considered to be the last of the true muscle cars.
Expect to pay $9,500 - $28,000 for an excellent basic Firebird Trans Am in this generation, and up to $50,000 for a 455, but only the 1973 model year.